There is an urgent need to understand the psychological and situational factors that influence adherence to highly active antiretroviral therapy (ART) among HIV+ Black men who have sex with men (BMSM) in the United States, notably those who engage in substance use. The objectives of the proposed study are to use interactive voice response (IVR) technology with twice daily phone diaries to explore how daily situational factors influence ART adherence and to develop a daily proactive planning (DPP) intervention that is tailored for use within this population, which has not, to date, been the targt of ART adherence interventions. Substance use is an important barrier to adherence among BMSM. It also occurs with greater frequency in MSM than in other groups in the U.S. Research suggests that to fully understand the effects of substance use on the well-being and health behaviors of MSM, studies must examine substance use behavior as it occurs at the daily, situational level. The proposed study will explore how daily fluctuations in substance use, affect, and stressful experiences and support (particularly experiences of acceptance/belonging and rejection/discrimination attributed to stigmatized identities including race, sexual orientation, ad HIV status) influence adherence to ART among HIV+ BMSM. Specifically, it will collect longitudinal data using a 3-week phone diary with a sample of 90 HIV+ BMSM aged 18-30 residing in New York City. By assessing participants on substance use, affect, and stressful experiences and support with twice-a-day phone diaries (one morning and one evening diary assessment) and on ART adherence with MEMS caps, the study can determine how changes in key variables influence adherence. Following the collection and analysis of longitudinal data, which will provide information on situation-behavior links, in-depth interviews focused on daily proactive planning will be conducted with a sub-sample of 10 master adherers, 10 inconsistent adherers, and 10 poor adherers. The quantitative and qualitative data will then be used to develop a brief, personally-tailored DPP intervention to improve adherence among substance-using HIV+ BMSM.